Field of the Invention
The present invention relates to a positive electrode active material used as a positive electrode material in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, and manufacturing process therefor, and to cobalt hydroxide particles which serve as a precursor for the positive electrode active material, and a manufacturing process therefor. Concretely, it relates to a lithium-cobalt composite oxide used as a positive electrode active material of lithium ion secondary battery, and manufacturing process therefor, and to hydroxide particles which serve as a precursor for the lithium-cobalt composite oxide, and a manufacturing process therefor. The present application claims priority based on the Japanese Patent Application No. 2014-020578 filed on Feb. 5, 2014 and Japanese Patent Application No. 2014-092601 filed on Apr. 28, 2014 in Japan.
Description of Related Art
Recently, smaller and lighter secondary batteries which have high energy densities have been required with popularization of mobile devices such as cellular phones and laptop personal computers. Such batteries include lithium ion secondary batteries using lithium, lithium alloy, metal oxide or carbon as negative electrode, and which have been actively researched and developed.
The lithium ion secondary batteries using lithium composite oxides, especially, relatively easily synthesized lithium-cobalt composite oxides for the positive electrode materials can achieve high voltages on the order of 4 V grade, so it is expected as batteries with high energy density, and have been progressively put into practical use. The lithium-cobalt composite oxides have characteristics that it is having high filling property compared to the other positive electrode active materials such as lithium-nickel composite oxides and lithium-nickel-cobalt-manganese composite oxides.
Generally, in order to improve the filling property of the positive electrode active materials, it is effective to improve a sphericity of the particles to be the positive electrode active materials, to improve the density of the particles itself, to have a proper width in the particle size distribution, to enlarge the particle diameter in proper range, and else. Also, the filling property of the positive electrode active materials tends to reflect the filling property of oxide itself, such as cobalt oxide, or of hydroxide itself, such as cobalt hydroxide, used as precursors for the positive electrode active materials.
With respect to the powder characteristic of the above hydroxide or oxide, for example in Patent Document 1 (D1), a cobalt oxide powder, wherein a particle shape of a cobalt oxide is approximately spherical, and 50% particle diameter (D50) is 1.5 to 15 μm, D90 is twice of D50 or less, D10 is ⅕ of D50 or more, and also, a specific surface area is 2 to 15 m2/g, is disclosed.
Also, in Patent Document 2 (D2), oxy-cobalt hydroxide particles, wherein a tapping density is 2.3 g/cm3 or more, and also, it is approximately spherical, and further, average particle diameter is 5 μm to 15 μm, is disclosed.
Further, in Patent Document 3 (D3), hydroxides of an alloy formed from a cobalt hydroxide or cobalt and the other metal, having a density of approximately 0.5 to 2.2 g/cm3, a particle diameter over approximately 1 μm, typically of approximately 1 to 20 μm, and a specific surface area of approximately 0.5 to 20 m2/g, is disclosed.
However, it cannot be said that the comprehensive consideration of particle property is sufficient for the hydroxides or oxides described in D1 to D3, and it cannot be said that the filling property of the obtained positive electrode active materials such as lithium-cobalt composite oxides will be sufficient.
On the other hand, in Patent Document 4 (D4), hydroxide cobalt particles in the shape of hexagonal prism, wherein average particle diameter of a bottom surface is 1 to 30 μm, and also, average particle height is 0.2 to 10 μm, is disclosed, but such shape with low aspect ratio is disadvantageous for the improvement of the filing property.
Further, in Patent Document 5 (D5), a manufacturing process of cobalt hydroxides, wherein the cobalt hydroxides are obtained by controlling a pH value in a tank in the range of 11.0 to 13.5, by maintaining a supply salt concentration, a supply salt flow rate, and a temperature in the tank, by continuously supplying and stirring an aqueous solution of cobalt salt and a caustic alkali solution in a same tank, is disclosed. In such continuous process, a particle size distribution will be spread wide, and it is considered to be effective for the improvement of the filling property, but it is having a problem in improvement of a cycle characteristics, so it cannot be said that the consideration for the filling property is sufficient.
As mentioned above, it is necessary to improve the filling property of the cobalt hydroxide particles which are precursors for the lithium cobalt composite oxides, in order to improve the filling property of the lithium cobalt composite oxides. However, the cobalt hydroxide particles described in D1 to D5 cannot achieve the sufficient filling property. Therefore, further improvement of the filling property of the cobalt hydroxide particles which will be precursors for the positive electrode active materials is desired.    Patent Document 1: JP 2001-354428 A    Patent Document 2: JP 2007-001809 A    Patent Document 3: JP 2003-503300 A    Patent Document 4: JP 1411-292549 A    Patent Document 5: JP H09-022692 A